Renal/Excretory System

Main purpose of excretory system

to maintain homeostasis by regulating electrolyte levels, amount of water in body, and ridding body of waste

How do sweat glands regulate temperature and remove waste

secrete water, dissolved salts, and nitrogenous waste (urea)

What does the liver break down

toxins, nitrogenous waste (excreted as urea), blood pigment waste (bilirubin)

What are the excretory organs/renal system?

kidneys, renal artery & vein, ureter, urinary bladder, urethra

Purpose of kidneys

filter blood to remove waste products

Purpose of renal artery and vein

carry blood to and away from kidneys for filtration

Purpose of ureter

duct for urine produced by the kidneys that drains into urinary bladder

Purpose of (urinary) bladder

stores urine before release

Urethra

tube that allows urine to pass outside the body

Layers of the kidney from OUTermost to INnermost

renal cortex, renal medulla, renal pelvis

Renal cortex

contains blood vessels and portions of the nephron (glomerulus)

Renal medulla

contains deeper portions of the nephron (loops of henle) and blood vessels

Renal pelvis

where fluid (urine) leaving excretory tubules is collected

Key things that take place in the excretory system

filtration, reabsorption, secretion, excretion

What happens in filtration

substances in blood are pushed across a filtration membrane into the kidney tubules (filtrate, most substances too big to pass through and remain in blood)

What happens in reabsorption

substances are moved out of kidney tubules and back into blood vessels (recovery of useful molecules)

What happens in secretion

substances are moved out of blood vessels into kidney tubules (no filtration membrane this time, gets rid of excess substances)

What happens in excretion

urination

Renal corpuscle

glomerulus surrounded by Bowman’s capsule where filtration occurs

Renal tubule

part of the nephron that leads away from renal corpuscle and into renal pelvis, including proximal convoluted tubule, loop of Henle, collecting duct

Glomerulus

network of capillaries with small pores that plasma is forced through utilizing hydrostatic/blood pressure (to the renal corpuscle)

Afferent vs efferent arterioles

carry blood TO vs AWAY from glomerulus (a-arrive, e-exit)

Bowman’s Capsule

cup shaped end of nephron surrounding glomerulus that fluid filtered from glomerulus has ro cross to enter the kidney tubules

layers of filtration membrane (glomerulus) from INnermost to OUTermost

glomerulus (capillary wall), basement membrane, podocytes (with foot process)

What substances pass through the capillary cells of the glomerulus AND podocyte foot processes into the kidney tubules but are almost completely reabsorbed into the blood

glucose and amino acids

Vasa recta

vessel network surrounding loop of Henle that helps maintain high salt concentration in medulla by returning substances back to bloodstream

What is absorbed (brought back into blood) at the proximal convoluted tubule?

glucose, amino acids, Na+, Cl-, K+, HCO3-, water (with solutes)

What is secreted (brought out of blood) at the proximal convoluted tubule?

drugs, toxins, urea, NH3, H+

Net result for filtrate in proximal convoluted tubule

volume is reduced but concentration remains same

Difference in processes of descending vs ascending loop of Henle

water reabsorption vs salt (Na+, Cl-) reabsorption

What does a longer loop of Henle result in

more opportunity to reabsorb water (present in desert animals)

How does salt concentration change from outermost to innermost layers of the kidney/nephron

increases (from cortex to outer medulla to inner medulla)

What is absorbed (brought back into blood) at the DISTAL convoluted tubule?

Na+, Cl-, Ca2+, water

What is secreted (brought back OUT of blood) at the DISTAL convoluted tubule?

K+, H+

Net result for filtrate in distal convoluted tubule

depends on hormone regulation

Sodium Chloride Cotransporter

moves sodium and chloride out of kidney tubule and back into blood with water, located in distal convoluted tubule

What is absorbed (brought back into blood) at the collecting duct?

Na+, Cl-, water, urea, HCO3-

What is secreted (brought back OUT of blood) at the collecting duct?

K+, H+, HCO3-

Net result for filtrate in collecting duct

depends on hormone regulation but generally increases in concentration

Where does urine go after the collecting duct

renal calyxes, renal pelvis, ureter

Hormone that increases water reabsorption

Antidiuretic Hormone (ADH)/vasopressin

Hormone that increases sodium absorption to regulate water & salt balance

Aldosterone

Where does ADH act

distal convoluted tubule and collecting duct of nephron by causing insertion of aquaporins into walls of tubule

Specialized tissue consisting of cells around the blood supply to the glomerulus (afferent and efferent arteriole) that regulate blood pressure

Juxtaglomerular Apparatus (JGA)

Types of cells in Juxtaglomerular Apparatus and their function

Macula densa (monitors blood pressure and volume by checking sodium chloride concentration, stimulates renin release when BP too low) and juxtaglomerular cells

How does the macula densa monitoring sodium chloride levels inform it of blood pressure

low blood pressure leads to low blood flow in kidneys, allowing sodium chloride to be absorbed more and lowering levels (indicating low BP)

Where does Aldosterone act

distal convoluted tubule and collecting duct by reabsorbing sodium (and water)

What does renin do

convert Angiotensinogen to Angiotensin I (releases ACE) to Angiotensin II, stimulating thirst, Aldosterone secretion, arteriole constriction, and ADH secretion (Renin-Angiotensin-Aldosterone System)

Common diuretics

coffee and alcohol, get rid of more water

How do diuretics work

diminish sodium reabsorption in nephron or block ADH receptors (both cause less water reabsorption)

Osmoregulation and excretion

process by which animals control solute concentration and balance water intake with water loss (along with regulating toxic metabolite ammonia)

Osmoregulation in marine fish

rarely urinate (very concentrated), constantly drink

Osmoregulation in freshwater fish

constantly urinate (very dilute), rarely drink (enters body by osmosis)

Nitrogenous waste in aquatic animals (fish)

ammonia

Nitrogenous waste in mammals, amphibians, sharks

urea

Nitrogenous waste in birds, reptiles, insects, snails

uric acid